This invention relates to a curable organopolysiloxane composition. In particular, the invention relates to an organopolysiloxane composition which is stable at room temperature without gelling but readily cures upon heating at elevated temperatures.
Heat curable organopolysiloxane compositions are known which comprise an organopolysiloxane having aliphatically unsaturated monovalent hydrocarbon groups bonded directly to the silicon atoms, an organohydrogenpolysiloxane having hydrogen atoms bonded directly to the silicon atoms and platinum or a platinum compound as a catalyst. The prior art organopolysiloxane compositions have a disadvantage in that they are prone to gelation even at room temperature during prolonged storage before use.
Several methods have been proposed to increase the stability of the organopolysiloxane compositions during storage by adding certain reagents to retard the crosslinking at room temperature. Several of the retarding agents used for this purpose in the art include tin compounds (see, for example, U.S. Pat. No. 3,532,649), isocyanurate compounds (see, for example U.S. Pat. No. 3,882,083), sulfoxide compounds (see, for example, U.S. Pat. No. 3,453,234), and aminosilanes (see, for example, U.S. Pat. No. 3,723,567).
Those prior art methods for the stabilization of the composition are disadvantageous in that that the the retarding agents must be used in large amounts and hence, the eventual decreases in the curing velocity result in difficult or insufficient cure of the composition even at elevated temperatures.
Further, acetylenically unsaturated compounds have been proposed as the retarding agents (see, for example, U.S. Pat. No. 3,445,420). The compounds have a boiling point in the range from 25.degree. C and 250.degree. C, and are free of nitrogen, carboxyl, phosphorus, mercapto groups, and carbonyl groups which are alpha to aliphatically unsaturated carbon atoms. The use of such acetylenic compounds is disadvantageous from the point of view that a compound having a relatively low boiling point tends to make the stability of the finished composition insufficient even at room temperature due to evaporation loss while, on the other hand, a compound having a relatively high boiling point brings about unsatisfactory cure to the finished compositions subjected to heating.